W A S H I N G T O N, Feb. 13 — One of the clearest signs the Bush administration is determined to get rid of Iraqi leader Saddam Hussein is that President Bush has now ordered the State Department, Pentagon and CIA to finalize plans to make this happen.

The plans include a variety of steps, ranging from diplomatic measures to providing U.S. military support for an armed Iraqi insurrection. If none of these measures succeeds — which is a real possibility — a large conventional U.S. ground force would be next. Sources tell ABCNEWS that the current war plan could require half a million troops, with at least 1,000 aircraft and six aircraft carriers. That plan is now being revised.Officials hope to exhaust other plans before sending troops into Iraq.

"I will reserve whatever options I have," Bush said today, when asked whether he was anticipating military action against Iraq. "I'll keep them close to my vest. Saddam Hussein needs to understand I'm serious about defending our country."

"How to achieve regime change — through opposition activity, military activity, other kinds of activity — all of those options are under consideration," Secretary of State Colin Powell reiterated today at a budget subcommittee at the House of Representatives.

First Step: Diplomacy

The first steps are diplomatic: trying to tighten sanctions and return United Nations weapons inspectors to Iraq, along with a broad campaign to line up reluctant allies for tougher moves to come.

Sources tell ABCNEWS the CIA is again spending money trying to encourage insurrection from within Iraq. As with the case in Afghanistan, the goal is to have locals do the brunt of the fighting.

But it almost certainly will take much more to overthrow Saddam. Officials say it probably will be necessary to arm and train the opposition in neighboring countries — like Kuwait and Turkey — a huge gamble for both nations.

The next step would be special operations troops joining Iraqi opposition forces inside the country. U.S. airstrikes would follow.

Officials stress no military action is likely for many months, though plans like these raise enormous questions: How many American casualties is the administration willing to lose? And what happens if Saddam is overthrown? Would this improve the situation or make it worse?

What has changed for the president, officials say, is his perception that the U.S. can no longer just wait for Saddam to build biological and chemical weapons and for him to then sell those weapons to terrorists. The plan now is to act before the Iraqi leader can.